The present invention generally relates to methods and apparatus for determining the fluid level of a container, such as an accumulator, and more specifically, to methods and apparatus for determining the fluid level of a container without the need for either electrical power or a direct line of sight to the container.
Accumulators are frequently used on military and commercial aircraft to accommodate the thermal expansion of coolant and hydraulic fluids. During aircraft servicing, maintenance personnel need to ascertain if the respective liquid loop contains the appropriate fluid level. Often, the accumulator is located in an inconvenient space for visual inspection and there is no aircraft electrical power available to operate a level sensor incorporating a rotary variable differential transformer (RVDT) or a potentiometer.
A measuring device for a tank is disclosed in U.S. Pat. No. 1,170,290. A float is attached to a rigid rod and as the float rises and falls, the rod moves in a linear direction. A vertical tubular member (guide tube) positioned inside the tank guides the movement of the rod. An indicator connected to the rod and positioned outside the tank determines the fluid level inside the tank. The rod and guide tube are positioned in a direct line of sight to the indicator. In an alternate embodiment, a chain is used in place of the rod. This device may not be useful for some applications because indicator placement requires a direct line of sight to the fluid container (tank). This requirement greatly limits the functionality and location of the remote indicator, especially in situations where the fluid container is almost surrounded by other components, beyond which a remote indicator is desired.
A fluid measuring device not requiring a direct line of sight between the fluid container and the indicator is disclosed in U.S. Pat. No. 1,266,743. The described device includes a float attached to a piano wire. The wire raises and lowers as the float raises and lowers. The wire is housed in a copper tube that can be bent to allow misalignment between the indicator and the liquid level. Although this method does not require a direct line of sight to the indicator, it may not be suitable for some applications. For some aircraft applications, for example, installation of the copper tube requires repeatedly bending and unbending the tube to position it around the various components. For some applications requiring complex routing scenarios through congested spaces, installation of the described device may be challenging.
As can be seen, there is a need for improved methods and apparatus for determining the fill level of a container, such as an accumulator, at a location more convenient for maintenance and without the need for electrical power or a direct line of sight to the accumulator.